Microplastics are a major source of environmental harm in the world today. Defined as plastic particles less than 5 millimetres in size, the tiny fragments are known to accumulate in our air, water, bodies and food as larger plastic sources degrade over time.
Trillions of plastic pieces now swirl in the world’s oceans, covering an astonishing 40 per cent of their surfaces. In terrestrial ecosystems, paint microplastics can make their way into rivers and lakes through stormwater runoff and wastewater discharge. Chemicals shed by plastic waste have been shown to have toxic effects on both marine life and human health.
And as ubiquitous as plastic is, so are its sources. Much has been written about the pollution caused by water bottles, food storage containers and plastic bags; in recent years, clothing fibres and tire dust have been added to the watchlist.
Now, environmental scientists at the Faculty of Arts & Science contend that another major source deserves more attention: paint.
A recent article published in the journal Environmental Toxicology & Chemistry highlights the particular risks of paint, which may even be the biggest contributor to microplastic pollution. It was co-authored by postdoctoral fellow Zoie Diana and MSc student Yuying Chen, as well as Chelsea Rochman, assistant professor in the Department of Ecology & Evolutionary Biology.
Diana says that paint may be severely underestimated as a pollutant, given that it can be hard to identify.
“Often, paint will show up as anthropogenic unknowns when characterizing microplastics,” she says. “Researchers have been wondering what such particles are and hypothesizing, based on computer modelling, that paint might be responsible for a large portion of them.”
Paint has not traditionally been considered a form of plastic, but on average, 37 per cent of it is composed of synthetic resins that bind pigments together. Diana is currently making a spectral library — a technique to identify the molecular structure of an unknown fragment — to fill that research gap.
The January 25 paper she co-authored, entitled “Paint: a ubiquitous yet disregarded piece of the microplastics puzzle”, also surveys existing literature to determine where paint pollution comes from.
“There’s paint from boats,” Diana says. “There’s also paint on buildings, on our roads. Once you walk around the city, you start to see it everywhere you look.”
Her team’s literature survey revealed that paint pollution is clearly understudied.
“There’s still a lot we need to learn about microplastics in general,” Diana says. “But as we mention in the paper, in 2019 alone there were about 800 studies published on the subject. So when we saw that only 53 primary studies had ever been done focusing on paint, we wanted to highlight that as a research gap. It’s a major component that has really been overlooked.”
Diana is currently completing a Liber Ero postdoctoral fellowship in the Rochman Lab. Prior to her arrival at U of T, she earned her PhD in marine science & conservation and integrated toxicology & environmental health at Duke University.
“The Liber Ero program is different from other postdocs, in that you work with both academic mentors as well as institutions and organizations,” she says. “The program supports academic research and also has global impacts beyond academia.”
A specialist in marine plastic pollution who’s now expanded her focus to include freshwater and estuaries, Diana says our near-complete dependence on plastic skyrocketed after World War II.
“Plastic started as a replacement for materials like ivory, for example, which was used for making things like combs and buttons. Obviously, a replacement for a natural resource like this was needed — but we’ve now gone overboard, and a lot of unnecessary plastic is being produced.”
However, she points out that much is currently being done to reduce microplastic pollution in general and is hopeful for a future in which paint pollution, too, can be reduced.
She points, for example, to rain gardens: landscape sites that absorb polluted stormwater.
“Rain gardens installed by major highways in San Francisco have been shown to reduce downstream microplastic emissions by 91 per cent, which is a really high success rate,” Diana says. “You can also install a filter in your washing machine that will capture microfibres before they’re passed along to the wastewater treatment plant.”
Where paint is concerned, special vacuums exist that can prevent paint emissions from spreading into the environment during building construction.
Diana is also optimistic that a global plastics treaty will be signed in the near future.
“That’s something that’s in the works, and I’m excited to see where it lands — particularly to reduce microplastics, which as we’ve seen are found everywhere.”